CN102226759A - Minim moisture detection system based on scanning method - Google Patents
Minim moisture detection system based on scanning method Download PDFInfo
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- CN102226759A CN102226759A CN 201110067146 CN201110067146A CN102226759A CN 102226759 A CN102226759 A CN 102226759A CN 201110067146 CN201110067146 CN 201110067146 CN 201110067146 A CN201110067146 A CN 201110067146A CN 102226759 A CN102226759 A CN 102226759A
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- distributed feedback
- photodetector
- feedback laser
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Abstract
The invention discloses a minim moisture detection system based on a scanning method, and belongs to the technical field of gas detection. The minim moisture detection system comprises a temperature control circuit, a current driving circuit, a distributed feedback (DFB) laser, a sawtooth wave generation circuit, an air chamber, a 1*2 coupler, a photodetector, a data acquisition card and a computer. The system is characterized in that: an output terminal of the DFB laser is connected with the 1*2 coupler through pigtail; two beam paths are connected with the rear of the 1*2 coupler, wherein one beam path is the photodetector, the other beam path is a beam path for cascade connection of the air chamber and the photodetector; the output terminals of the photodetectors in the two beam paths are respectively connected to the data acquisition card; the output terminal of the data acquisition card is connected with the computer; the sawtooth wave generation circuit is connected with the current driving circuit and is connected with the DFB laser; the temperature control circuit is connected to the DFB laser. The system has advantages of resist radiation, corrosion proof, anti-electromagnetic interference, on-line monitoring, small volume of required gas, simple operation, short response time and high accuracy.
Description
Technical field
The present invention relates to a kind of gas detecting system, specifically is a kind of little water detection system based on scanning method, belongs to the gas detection technology field.
Background technology
Steam exists in the multiple gases, such as air, and rock gas and oxygen or the like.When we use these gases in the specific environment, we are just relatively stricter to the concentration requirement of the steam in these gases, too much steam may crisis to the safety of lives and properties:
(1) employed pressurized air of medical industry patient care and gas must be the cleaning with sterilized.The concentration index of main contaminants has life-and-death importance in the monitoring gas.If concentration is not monitored, will damage patient's health.These contaminants comprise carbon monoxide and carbon dioxide, oxides of nitrogen, oil and the steam in the gas.Under the steam situation, there are two phenomenons to treat cautiously.The one, potential condensation in the gas system can cause the interference to water liquid in the crucial apparatus, and to the potential corrosion of gas system part.The second, the harmful bacteria hobby is in the occasion breeding of high humility, and too much steam condensation has the effect of adding fuel to the flames to the growth of bacterium, thereby entail dangers to is breathed the patient of medical gas.
(2) SF6 gas has good insulation performance performance and arc extinction performance, and present stage is widely used in the high voltage electric equipment, under nominal situation, is comparatively desirable insulation and arc-extinguishing medium.The height of its operating air pressure and micro-water content has direct influence to the safe and reliable work of equipment, if SF6 gas leak cause density to descend or gas in micro-water content exceed standard, will there be potential safety hazard in high voltage electric equipment even causes accident to take place.Therefore the monitoring to SF6 high voltage electric equipment gas density and micro-water content is that relevant industries are to one of monitoring of equipment important ingredient always.
(3) rock gas is one of most important energy in the world today.Rock gas is outwards needing to carry out purified treatment before the transmission.Moisture is one of pollutant important in the rock gas, all needs to monitor in real time moisture in the purified treatment of rock gas and each stage of transmission.Too much moisture can cause the formation of hyrate in the pipeline and the corrosion of transport pipeline.This may cause serious security incident and expensive stopping transportation cost.Thereby too much moisture also can dilute calorific value and quality that rock gas reduces rock gas.
Owing to the rise of Gas Prices and all over the world to the quick growth of Natural Gas Demand, the processing of liquefied natural gas (LNG) and transmission have obtained increasing concern.Moisture in the rock gas freezes in sub zero treatment equipment and can damage liquefaction and gas booster compressor, therefore needs accurately to monitor and control moisture in processes such as the pre-service of liquefied natural gas (LNG), cooling, pressurization.
All occasions make us know the necessity that detects vapour concentration, and traditional method has minute surface method, gravimetric method, coulomb electrolytic process, capacitance method etc.What these measuring methods had requires than higher environmental baseline, and the time of measurement is long, is afraid of to pollute etc., and air consumption is bigger during the measurement that has, equipment also need to switch in advance ventilation drying and poor repeatability during use.Promptly belong to these row as { Proceedings of the CSEE } the 23rd volume the 10th phase (in October, 2003) by " discussion of SF6 gas water management standard and the research of density and humidity detection " that Li Taijun, Wang Zhangqi, Zhang Ting, Liu Quan will are write.
Summary of the invention
For overcoming the deficiencies in the prior art and defective, the present invention proposes a kind of little water detection system based on scanning method, measure the concentration of steam by the ratio of transmitted light intensity after the gas absorption and input light intensity.
Technical scheme of the present invention realizes in the following manner:
A kind of little water detection system based on scanning method, comprise Distributed Feedback Laser, 1*2 coupling mechanism, air chamber, photodetector, data collecting card, computing machine, saw-tooth wave generating circuit, temperature control circuit and current driving circuit, it is characterized in that the output terminal of Distributed Feedback Laser inserts the 1*2 coupling mechanism through its tail optical fiber; 1*2 coupling mechanism back connects the two-way light path through ordinary optic fibre respectively, wherein one the tunnel is photodetector, another road is the serial connection light path that air chamber is followed photodetector, the output terminal of the photodetector in two light paths is electrically connected to respectively on the data collecting card, and the output terminal of data collecting card is connected with computing machine; Saw-tooth wave generating circuit is connected to current driving circuit and is connected with Distributed Feedback Laser; It is constant with the temperature maintenance of control Distributed Feedback Laser that temperature control circuit is connected to Distributed Feedback Laser.
It is the Distributed Feedback Laser of 1370nm that described Distributed Feedback Laser adopts wavelength.
Above-mentioned Distributed Feedback Laser is the abbreviation of English Distributed Feedback Laser, i.e. distributed feedback laser, and it is built-in Bragg grating (Bragg Grating), belongs to the semiconductor laser of side-emitted.The maximum characteristics of Distributed Feedback Laser are to have extraordinary monochromaticity (being spectral purity).
The course of work of detection system of the present invention is as follows: the Distributed Feedback Laser emitting laser enters the 1*2 coupling mechanism through tail optical fiber, be divided into two-way, one the tunnel directly enters photodetector, another road enters air chamber, part light intensity is by water vapor absorption, the light that comes out from air chamber enters and enters photodetector again, this two ways of optical signals all is converted into electric signal at last, enter data collecting card at last, they are carried out the information data collection, just gather, again to their calculating such as be divided by to incident intensity with through the transmitted light intensity after the gas absorption, get the light intensity ratio at absorption peak place, finally obtain the concentration of steam by Lambert law.The steady temperature of temperature control circuit control Distributed Feedback Laser, make not temperature influence of laser output wavelength, by the sweep frequency of current driving circuit and saw-tooth wave generating circuit control laser instrument, make the width range of its sweep limit again greater than tested gas absorption spectrum line.
Concrete action principle of the present invention is as follows: any medium, electromagnetic wave energy to various wavelength can absorb more or less, the absolute transparent medium that does not absorb is non-existent fully. gas is no exception, light to certain wavelength also has absorption. and every kind of gas molecule all has the absorption spectra feature of oneself, the light wavelength difference of the gas of different molecular structures to being absorbed.
Wherein the most basic principle is exactly the Beer-Lambert law
I＝I
0exp[-α(V)CL]
Wherein, the transmitted light intensity of I after to be light by medium absorb in the formula;
I
0The light intensity of incident medium (inciding the light intensity that the light intensity on the medium promptly absorbs without medium);
α (V) is an absorption coefficient, and promptly gas is in the absorption line style at certain frequency V place;
C is a gas concentration;
L is the total length in gas absorption path.
When x is smaller, e
-x≈ 1-x is so following formula can draw C=(1-I/I as calculated
0)/(α (v) L)
Under certain temperature, pressure and light frequency, α (V) can find by database, L can measure, can see thus as long as we are under the prerequisite of uniform temperature and pressure, gather incident intensity and transmitted light intensity through data collecting card, and, calculate the concentration that just can draw steam by Lambert law again through calculating the ratio of transmitted light intensity and incident intensity.
Cause is in gas absorption peak value place, gas absorption rate
Have maximum value, signal is extracted easily, therefore the concentration that adopts the gas absorption peak to come probe gas usually.
Obtain by database, at 1365～1370nm wave band, vapour molecule has the strongest absorption when 1368.6nm, and near the absorption line of the no background gas component of this absorption line wavelength, thereby avoid the background gas component that the intersection of tested gas is absorbed interference, guarantee the accuracy of measuring.
The emission wavelength of Distributed Feedback Laser is relevant with temperature and drive current, can come the modulated laser wavelength by temperature and the drive current of regulating semiconductor laser.We adopt wavelength is the Distributed Feedback Laser of 1370nm, by regulating temperature control circuit, make the about 1368.6nm of its output wavelength, make it temperature-resistant by temperature control circuit, eliminate the influence of temperature to laser output wavelength, under the temperature constant condition, light and its drive current size sent from distributed feedback type semiconductor laser (DFB) are approximated to linear relationship, driving by current driving circuit and saw-tooth wave generating circuit again, make laser instrument become tunable laser, and make the width of the sweep limit of laser instrument greater than tested gas absorption spectrum line, make fully absorbing light of gas, peak value is absorbed.
Pass through photodetector at last, make incident intensity and transmitted light intensity convert electric signal to, through data collecting card these two kinds of signals are gathered again, pass through accurate calculating on computers, get the ratio that absorption peak goes out, draw the concentration of gas by Lambert law.
The present invention has following advantage: the present invention carries out sensing by optical fiber, and the energy radioresistance is anticorrosive, be not subjected to the influence of environment, can move yet, can eliminate the de-stabilising effect of light source at the high temperature rugged environment, degree of accuracy is also than higher, and relatively sensitiveer, the response time is shorter, can in time obtain the concentration of steam, easy and simple to handle, pollution-free, as long as change wavelength coverage, this way can be applied in the detection of other kind gas concentrations and go simultaneously, uses very extensive.
Description of drawings
Fig. 1 is the structural representation of system of the present invention.
Wherein: 1, saw-tooth wave generating circuit, 2, current driving circuit, 3, temperature control circuit, 4, Distributed Feedback Laser, 5, the 1*2 coupling mechanism, 6, photodetector, 7, air chamber, 8, photodetector, 9, data collecting card, 10, computing machine, 11, ordinary optic fibre.
Embodiment
The present invention will be further described below in conjunction with drawings and Examples, but be not limited thereto.
Embodiment:
The invention process is for example shown in the system diagram 1: comprise Distributed Feedback Laser 4,1*2 coupling mechanism 5, air chamber 7, photodetector 6,8, data collecting card 9, computing machine 10, saw-tooth wave generating circuit 1, temperature control circuit 3 and current driving circuit 2, it is characterized in that the output terminal of Distributed Feedback Laser 4 inserts 1*2 coupling mechanism 5 through its tail optical fiber; 1*2 coupling mechanism 5 back connect the two-way light path through ordinary optic fibre 11 respectively, wherein one the tunnel is photodetector 6, another road is the serial connection light path of air chamber 7 with photodetector 8, the output terminal of the photodetector 6,8 in two light paths is electrically connected to respectively on the data collecting card 9, and the output terminal of data collecting card 9 is connected with computing machine phase 10; Saw-tooth wave generating circuit 1 is connected to current driving circuit 2 and is connected with Distributed Feedback Laser 4; It is constant with the temperature maintenance of control Distributed Feedback Laser 4 that temperature control circuit 3 is connected to Distributed Feedback Laser 4.
It is the Distributed Feedback Laser of 1370nm that described Distributed Feedback Laser adopts wavelength.
Claims (2)
1. little water detection system based on scanning method, comprise Distributed Feedback Laser, 1*2 coupling mechanism, air chamber, photodetector, data collecting card, computing machine, saw-tooth wave generating circuit, temperature control circuit and current driving circuit, it is characterized in that the output terminal of Distributed Feedback Laser inserts the 1*2 coupling mechanism through its tail optical fiber; 1*2 coupling mechanism back connects the two-way light path through ordinary optic fibre respectively, wherein one the tunnel is photodetector, another road is the serial connection light path that air chamber is followed photodetector, the output terminal of the photodetector in two light paths is electrically connected to respectively on the data collecting card, and the output terminal of data collecting card is connected with computing machine; Saw-tooth wave generating circuit is connected to current driving circuit and is connected with Distributed Feedback Laser; It is constant with the temperature maintenance of control Distributed Feedback Laser that temperature control circuit is connected to Distributed Feedback Laser.
2. a kind of little water detection system based on scanning method as claimed in claim 1 is characterized in that it is the Distributed Feedback Laser of 1370nm that described Distributed Feedback Laser adopts wavelength.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103411902A (en) * | 2013-07-22 | 2013-11-27 | 山东大学 | Wide-range micro-water measuring system based on programmable amplifier |
| CN103472003A (en) * | 2013-09-27 | 2013-12-25 | 山东大学 | Novel method used for phase lock voltage subtraction of micro water vapor detection |
| CN105203460A (en) * | 2015-10-27 | 2015-12-30 | 中国科学院合肥物质科学研究院 | Infrared laser spectrum system for detecting trace quantity of water steam, and detection method thereof |
| CN104280362B (en) * | 2014-09-22 | 2017-04-05 | 合肥工业大学 | A kind of superheated vapor laser spectrum on-line detecting system |
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| US6787776B2 (en) * | 2001-08-16 | 2004-09-07 | The Board Of Trustees Of Leland Stanford Junior University | Gas sensor for ammonia, carbon dioxide and water |
| US20030132389A1 (en) * | 2002-01-17 | 2003-07-17 | Von Drasek William A. | Method for monitoring and controlling the high temperature reducing combustion atmosphere |
| US7259856B2 (en) * | 2005-02-16 | 2007-08-21 | Picarro, Inc. | Method for the precise measurement of the wavelength of light |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103411902A (en) * | 2013-07-22 | 2013-11-27 | 山东大学 | Wide-range micro-water measuring system based on programmable amplifier |
| CN103472003A (en) * | 2013-09-27 | 2013-12-25 | 山东大学 | Novel method used for phase lock voltage subtraction of micro water vapor detection |
| CN104280362B (en) * | 2014-09-22 | 2017-04-05 | 合肥工业大学 | A kind of superheated vapor laser spectrum on-line detecting system |
| CN105203460A (en) * | 2015-10-27 | 2015-12-30 | 中国科学院合肥物质科学研究院 | Infrared laser spectrum system for detecting trace quantity of water steam, and detection method thereof |
| CN105203460B (en) * | 2015-10-27 | 2018-01-12 | 中国科学院合肥物质科学研究院 | Infrared laser spectroscopy trace steam detecting system and its detection method |
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Application publication date: 20111026 |